Charles H. Spurgeon on Psalms 140:3

They have sharpened their tongues like a serpent. This is an exact description of the way in which a serpent darts out his tongue before he inflicts the wound. See him: his head is erect, and his piercing eye is wildly and fiercely fixed on the object; the tongue rapidly appears and disappears, as if by that process it would be sharpened for the contest. Thus were the enemies of David making sharp their tongues for his destruction. —Joseph Roberts, in "Oriental Illustrations of the Sacred Scriptures," 1835.